||The design of long term nuclear waste repositories includes the building of an engineered barrier around the waste containers, which aims to create a “low permeable zone” around them (Komine, 2004; Alonso et al., 2006). Bentonite clay has been chosen by several industrialized countries as a buffer and backfill material to separate radioactive waste from the surrounding host rock. Its main properties are an extremely low permeability, a self-healing ability, low ion transport capacity and high chemical stability, together with high expandability and faire ductility (Kaufhold et al., 2007).
In situ, after water uptake from the host rock, sealing will be obtained gradually due to bentonite swelling. It will fill the entire space between the buffer material and the disposal pit wall. Meanwhile, formation of gas, mainly hydrogen, due to humid corrosion, degradation of organic matter or water radiolysis, is unavoidable within galleries (Birgersson et al., 2008). If gas production rate is higher than what can be expelled by diffusion via the claystone barrier pores, gas will accumulate into the void space of the engineered barrier until its pressure becomes large enough to enter the clay and then, it may leak from the repository, together with radionuclides.
In this context, this contribution presents an experimental investigation of bentonite–sand plug swelling pressure and kinetics, and of its gas breakthrough pressure, in presence of both water (obtained by contact with fully water–saturated bentonite) on one side, and gas pressure, at either 0, 4 or 8MPa, on the other side. This laboratory experiment mimics the PGZ in situ experiment launched by Andra in the underground facility at Bure (France).